What is the monsoon?

Come June, everyone is talking about the monsoon – When will it come? Will it be on time? Will there be enough rain for crops? The monsoon is one of the most important weather patterns in India. The lives of many people depend on it. But, why is the monsoon so important? And how is it formed? Let’s find out.

How does the monsoon occur?

The monsoon basically refers to big winds. During summer, the landmass of India becomes very hot. This creates an area of low pressure above the land. The low pressure attracts or pulls in wind from the nearby ocean.

These winds from the ocean are very cool and they contain water drops in the form of clouds. As the winds reach India, they encounter high mountains – such as the Western Ghats on the west coast and then further inside, the high Himalayas. These mountains stop the winds from going any further – the clouds therefore shed their rain over India. This is how the monsoon takes place.

Two kinds of monsoons

In India, we see two kinds of monsoons:

South-west Monsoon

The south-west monsoon takes place between June and September. During these months, most parts of India, including cities such as Delhi, Mumbai and Kolkata get rainfall.

During the south-west monsoon, cities like Mumbai get a lot of rain. Sometimes, there is so much rain that it causes floods!

North-east Monsoon

The north-east monsoon takes place between October and December. During this time, states such as Tamil Nadu and Andra Pradesh get rainfall. But this monsoon is much smaller than the South-west monsoon.

The north-east monsoon is very important for the growth of rice (see paddy fields to the right) in the states of Tamil Nadu and Andhra Pradesh.

How is the monsoon predicted?

For nearly 150 years, the Government of India has been trying to predict the monsoon (to predict means to make a guess about what will happen in the future). Each year, meteorologists (scientists who study weather) from the Indian Meteorological Department (IMD) try to predict when the monsoon will arrive and whether it will be normal. To predict the monsoon, scientists study pre-monsoon (the period before it starts raining) weather patterns and details of monsoon rainfall for the last 20-25 years.

What is a normal monsoon?

You may have read or heard weather reports that say that the rainfall was less or more than “normal.” What does this mean? Well, based on the rainfall patterns over many years, scientists know the usual amount of rainfall that India gets from each monsoon. If it rains the same amount this year, then we will say that India had a normal monsoon in 2011.

How is rainfall measured?

Rainfall is measured in millimeters or ‘mm’. Say, for example, Delhi received around 60 mm rain on one day. This means that each square metre of land in Delhi received 60 litres of rain water. (If you put two study desks together to create a square you will create an area that roughly equal to one square metre. Now imagine 60 litres of water filling that!). To measure rainfall, we use an instrument called a rain gauge.

Why is the monsoon so important?

The monsoon is very important for India. That’s because of the following reasons:

Farmers depend on rain for their crops. Most the agriculture in India depends on rainfall to water crops.

Many of the crops grown in India depend on the monsoon for water. When the monsoon is less than normal, farmers grow fewer crops. While they earn less, this also means there is less food for everyone. When there is less food than what we need, food becomes costly. Prices of rice, wheat and other food items go up.

The monsoon is the most important source of freshwater for India. It fills up rivers and lakes which supply us with water

The monsoon is also important to animals and plants that live and grow near water